The high order multi-antenna technology is one of the critical technologies of the long term evolution advanced (LTE-A or LTE-Advanced) system for improving the transmission rate of the system. In order to achieve channel quality measurement and data demodulation after the high order multi-antenna technology is introduced, the LTE-Advanced system respectively defines two types of pilot symbols: demodulation reference symbol (DMRS) and channel quality measurement-reference symbol (CSI-RS), wherein the demodulation reference symbol is a reference symbol used for the demodulation of a physical downlink shared channel (PDSCH). The measurement reference symbol is a reference symbol used for measuring channel state information (CSI) and also for reporting information such as channel quality indicatior (CQI), pre-coding matrix indicator (PMI), and rank indicator (RI). The structures of the above two types of reference symbols can be used for supporting new technologies of LTE-A such as coordinated multi-point (CoMP), spatial multiplexing, etc.
In the LTE, a common reference signal (or cell-specific reference signal, CRS) is used for pilot measurement, that is, all the users use the common pilot to carry out channel estimation. Such common reference signal requires the transmission side to notify the receiving end which preprocessing manner is used on the transmitted data, and also the overhead is considerable; furthermore, in a multi-user multi-input multi-output (MU-MIMO) system, since a plurality of user equipment (UE) use the same CRS, the orthogonality of pilots cannot be realized, and the interference cannot be estimated.
In the LTE-A, in order to reduce the pilot overhead, the channel quality measurement reference symbol and demodulation reference symbol are designed separately, and the demodulation reference signal and data employ the same pre-processing manner. At the same time, the demodulation reference symbol is mapped according to the available rank information of the corresponding channel of a scheduling user, therefore, the overhead can be adjusted in a self-adaptive way according to the rank information so that the overhead can be greatly reduced in the case where the rank is relatively low.
In the current discussion, the design pattern of the demodulation reference symbol has already been determined, as shown in FIGS. 1(a), 1(b) and 1(c), when the rank used by downlink transmission is less than or equal to 2, the resource unit indicated by  is merely used for the transmission of DMRS and the scrambling is carried out on two adjacent Orthogonal Frequency Division Multiplexing (OFDM) symbols in time domain by using an orthogonal cover code (OCC) with the length thereof being 2. The  in FIGS. 1(a), 1(b) and 1(c) represents common reference signal (CRS).
When the rank is greater than or equal to 3 and less than or equal to 4, two groups of resource units (RE) are used, respectively shown as  and . In this case, orthogonal code division multiplexing (CDM) can be carried out on 2 layers of DMRS at most on each group of RE, and each group of RE carries out orthogonal scrambling on two adjacent OFDM symbols in time domain by using an orthogonal cover code with the length thereof being 2. When the rank is greater than 4, for two groups of RE (as shown by  and ), each group carries out orthogonal scrambling in the direction of time domain by using an OCC code with the length thereof being 4 and the maximum number of orthogonal CDM multiplexing DMRS layers is 4 in each group of RE.
In addition, currently in the case of single-user multi-input multi-output (SU-MIMO), the mapping manner from codeword stream to layer defines the situation of different numbers of layers, as shown in FIG. 2.
In LTE-A, in order to support 8-layer transmission at most, it needs to at most define 8 DMRS ports, indicated as DMRS port 7, 8, 9, 10, 11, 12, 13 and 14. In this case, the DMRS port is an antenna port defined on layer, corresponding to the layer of data transport, and it is used for estimating the equivalent channel of the data of each layer during space transmission.
However, when the UE side carries out data demodulation, in order to be able to carry out demodulation, it is necessary to determine that the DMRS corresponding to which DMRS ports occupies the same group of resources, and to carry out code division multiplexing, and use the relationship between the data layer and the demodulation reference symbol port, so as to estimate the channel information of the corresponding layer and carry out the detection.